1. Field of the Invention
The present invention is related to metal oxide-containing nanoparticles and to methods of making said metal oxide-containing nanoparticles; and in particular to copper oxide-containing nanoparticles that are reducible to copper metal by heating or by contacting with a reducing agent.
2. Background Art
Semiconductor technology increasingly requires the fabrication of faster and more densely packed integrated circuits. This increasing demand necessitates better control of conductive interconnects. Of particular interest is the formation of interconnects in trenches with high aspect ratios. It is anticipated that aspect ratios of 1.9 or higher will be required within the next decade. Currently, the most common methods of forming interconnects are by physical vapor deposition, chemical vapor deposition, or electrochemical deposition. Aluminum and copper are the most common metals used for this purpose. In the typical application, trenches and other structures are overfilled with copper. Wafers treated in such a manner are then subjected to chemical mechanical polishing which is somewhat tedious and causes the surface of the interconnect to be curved. Moreover, each of these techniques is somewhat susceptible to defects. More importantly, the vacuum coating technologies such as physical vapor deposition and chemical vapor deposition require significant capital equipment costs and are not able to achieve very high aspect ratios.
Metal nanoparticles have been recognized as potentially useful in forming conductive interconnects in such semiconductor devices. The nanoparticle size range is typically taken to be from about 1 nm to about 100 nm. Particles of such dimensions exhibit unusual properties which may advantageously be applied when forming interconnects. Although such nanoparticles exhibit some collective atomic behavior, surface and quantum effects may be important. The lower melting points of nanosized metal particles make such particles attractive for interconnect technology. Such reduction in melting point can be over 500° C. with melting points of less than 350° C. attainable for many nanosized metals. In the typical application, a dispersed solution containing the nanoparticles is applied to a substrate having trenches by spin coating or some other dispersal technique. The nanoparticles will preferentially aggregate in the trenches. The substrate is then heated to sinter and/or melt the nanoparticles together thereby forming the interconnect.
U.S. patent application No. 20030008145 discloses a method of malting metal nanocrystals that include passivating ligands. The metal nanoparticles of this application have enhanced solubility and/or dispersion because of the passivating ligands associated with the nanocrystals. However, metal containing nanoparticles are somewhat undesirable because of the increased reactivity of such particles and in particular to the potentially violent oxidation reaction that may occur in the presence of oxygen, water, or certain organic compounds.
Accordingly, there exists a need in the prior art for improved methods of making metal interconnects and for precursors for making such interconnects that are both economical and stable.